(1) Field of the invention
This invention relates to novel compositions of matter and particularly to compositions which comprise a graphite framework which is intercalated by one or more buckminsterfullerene species and optionally by other additional chemical species. Methods for preparation of the compositions are disclosed.
(2) Description of the prior art
Elemental carbon occurs throughout the universe in different allotropic forms. Two of the allotropes which are frequently encountered are graphite and diamond. In their purest forms, these materials are composed entirely of carbon atoms, and the differences in their physical and chemical properties arise from differences in the arrangement and bonding between the carbon atoms they comprise. For example, diamond is known to exist with a cubic structure built up from sp3-hybridized tetrahedrally arranged carbon atoms. The lattice layers follow the sequence, ABCABC.
The structure of graphite has been known for quite some time. See "The Nature of the Chemical Bond" by Linus Pauling, third edition, pages 234-235. Graphite is a layered structure containing stacked layers or "sheets" of sp2-hybridized carbon atoms. The carbon atoms within a given layer are configured in a planar hexagonal array with each individual carbon atom being strongly bonded to its three neighboring carbon atoms. Adjacent layers are held together by chemical forces which are much weaker than those which bond the carbon atoms within a given layer to one another. Accordingly, the distance between carbon atoms within a given layer is much less than the distance between the adjacent layers. The distance between adjacent layers is about 3.35 Angstrom units, while the distance between individual carbon atoms within a given layer is about 1.4 Angstrom units. It is generally accepted that the sliding motion of the sheets over one another gives rise to the observed lubricity of graphite.
Amorphous carbons which include soots, carbon black, charcoals, lampblack and the like are all microcrystalline forms of graphite. The macroscopic properties of these materials depend upon their particle size and surface area. Amorphous carbons are frequently employed as support materials for noble metal and other catalysts. Other forms of graphite include fibers, foams, foils, and whiskers.
Another family of allotropes of elemental carbon known as "buckminsterfullerenes" exist wherein the individual carbon atoms are bonded to one another so as to take on the shape of truncated icosahedra. Such materials are conveniently pictured as graphite sheets which have been wrapped around themselves or manipulated so as to form a closed sphere. The 3-dimensional structure formed by the carbon atoms of such materials resembles a spherical cage or shell. Generally, the molecules of the buckminsterfullerenes are reminiscent of a soccerball, since they are roughly spheroidal and comprise both pentagonal and hexagonal rings of carbon atoms as units from which they are built up. Allotropic homonuclear buckminsterfullerene-type spheroids comprising 60, 70, 84, and higher analogous species containing larger numbers of carbon atoms in the form of a cage structure are known. The simplest such structure, containing 60 carbon atoms, has been described in the publication entitled, "Nature" in volume 318, page 162. Other buckminsterfullerenes are described in the following publications and are incorporated herein by reference: "Chemical and Engineering News", Oct. 29, 1990 issue, pages 22-25; "Journal of Physical Chemistry" Vol. 94, pages 8634-8636 (1990); Nature, Volume 350, Mar. 7, 1991; and "Scientific American", Oct. 1991 issue.
Pure carbon in its various known allotropic forms provides many currently-useful and many potentially useful commercial and research applications. For example, the high thermal conductivity of diamond along with its electrically insulative properties allows its widespread use as a heat sink material for certain solid state devices in the microelectronics industry. Graphite has been used successfully as a lubricant and a catalyst support material. Various carbons have also found use as electrically resistive compositions commonly found in many types of electrical components. Additionally, it has been observed that the 60-carbon atom buckminsterfullerene becomes a superconductor at 18 degrees K when doped with potassium. (See "Science" 252, 1154 (1991).